This invention generally relates to color television (video) cameras, and particularly the present invention relates to color television cameras having a color separation crossing striped filter in the light path thereof.
Color television cameras (television will be simply referred to as TV hereafter) are arranged to obtain a multicolor TV signal as an output signal of a pickup tube by using a color separation striped filter. This filter, having a given pattern, is positioned in the light path between the subject and the photoelectric convertion surface of a pickup tube. At the output of the filter, a signal is disclosed having a given spatial frequency in accordance with the details of the repetitive arrangement of color stripes of the color separation striped filter. The output signal of the pickup tube is in the form of a signal modulated by the color signal.
Therefore, the signal having the given spatial frequency above-mentioned color separation striped filter, interfers with a signal obtained from the subject, and thus, beat interference undesirably occurs in the reproduced picture.
Up to this time, in order to resolve this problem the above-mentioned beat interference has been removed or reduced such that, as proposed in e.g., Japanese Patent Publication 43-1910, an optical image of a subject having a applied pattern is given to the photoelectric conversion surface of the pickup tube under the condition that the image has been defocused only in the direction of the scanning line, by using a lenticular lens, phase grating plate or the like. As proposed in Japanese Utility Model Publication 47-18688, an optical image of a subject having a applied pattern is given to the photoelectric conversion surface of the pickup tube under the condition that the image has been defocused only in the direction of the scanning line, by using a flat surface of a transparent anisotropic substance (such as a flat plate of crystal). This substance develops double refraction characteristics as an optical interdigital filter. As such, the spatial frequency in accordance with the given repetitive arrangement of the color stripes of the color separation striped filter and a frequency which is an odd multiple of the spatial frequency are the peak attenuation points thereof, while zero spatial frequency and even multiples of the spatial frequency are the transmission range thereof.
The above-mentioned resolving technique is effective when the color separation striped filter has a structure such that vertically extending color stripes of the filter are arranged in the direction of the scanning line (horizontal direction) in a given repetitive order. However, when the color separation striped filter is of a crossing type, beat interference occuring in the reproduced picture cannot be satisfactorily removed or reduced because the number of patterns of a subject, which cause the occurrence of beat interference in the reproduced picture in connection with the pattern of the color separation crossing striped filter, is more than one.